The agreement, with guarantees near $50 million, is by far the biggest in the franchise's history and could keep the star receiver with the team through the 2018 season.
The six additional years after 2012 would be worth $17 million each.
The $15 million average would tie him with the Raiders' Richard Seymour for the fifth-highest average among all players. The top four players are all quarterbacks.
Fitzgerald and team president Michael Bidwill appeared at a hastily called news conference Saturday night to announce the agreement.
Fitzgerald insisted he "hates this part of sports," but he certainly has made a boatload of money. This is the third major contract he has signed, and he doesn't turn 28 until Aug. 31.
"Growing up, since I was 7 years old, this has been the game I love and something I have been so passionate about," Fitzgerald said, "and to have to talk about it on the business side is a little bit uncomfortable. But I am really happy to put it behind us and it wouldn't be possible if it wasn't for the Bidwill family's hard work in making this thing happen."
The Cardinals had said they wanted Fitzgerald's new contract wrapped up by the start of the regular season, and they made it with two weeks to spare.
Bidwill, son of the team's owner Bill Bidwill, said the Cardinals' intent is to have Fitzgerald retire as a Cardinal "but not anytime soon."
Fitzgerald, the third overall park in the 2004 draft at the age of 19, spoke of the opportunity to spend his entire career with one team.
"It is an honor," he said. "I am so fortunate. Not many players have that opportunity but Michael has allowed me that opportunity and I just want to repay him with great effort and winning. That is what is important."
The 6-foot-3, 218-pound receiver has become the franchise's career leader in receptions with 613 and needs just 294 yards to surpass Roy Green for career yards receiving. In Arizona's surprise run to the Super Bowl in the 2008 season, Fitzgerald shattered most of the NFL playoff receiving records.
Fitzgerald has topped 1,000 yards receiving in five of his seven NFL seasons, including the last four. He caught 90 passes for 1,137 yards last season even though Arizona had one of the worst offenses in the league while struggling to a 5-11 record, in large part because of poor quarterback play in the wake of the retirement of Kurt Warner.
While Fitzgerald said he never insisted the team make a big move for a quarterback -- "I am not anyone to hold a hammer over anyone's head" -- the Cardinals traded for Kevin Kolb from the Philadelphia Eagles, then signed him to a five-year, $63 million contract, with $21 million guaranteed. Fitzgerald, who organized team workouts during the lockout, had a practice session with Kolb long before the trade.
It is not known whether the deal contains the kind of terms that gave him huge leverage over the team under its current deal -- specifically a ban on making him a franchise player and a no-trade clause.
Johnson tweeted "congratulations to @LarryFitzgerald god is good" and Fitzgerald responded with "thanks CJ you up next my guy."
ESPN NFL Insider Adam Schefter and ESPN.com senior writer John Clayton contributed to this report.